Marine Antifreeze Proteins: Structure, Function, and Application to Cryopreservation as a Potential Cryoprotectant

Cryoprotective Polysaccharides with Ordered Gel Structures Induce Ice Growth Anticipation and Survival Enhancement during Cell Cryopreservation

This work cross-correlated rheological, thermodynamic, and conformational features of several natural polysaccharides to their cryoprotective performance. The basis of cryoprotection of FucoPol, pectin, and agar revealed a causal combination of (i) an emerging sol-gel transition (p = 0.014) at near-hypothermia (4 °C), (ii) noncolligative attenuated supercooling of the kinetic freezing point of water (p = 0.026) supporting ice growth anticipation, and (iii) increased conformational order (p < 0.0001), where helix-/sheet-like features boost cryoprotection. FucoPol, of highest cryoprotective performance, revealed a predominantly helical structure (α/β = 1.5) capable of forming a gel state at 4 °C and the highest degree of supercooling attenuation (TH = 6.2 °C). Ice growth anticipation with gel-like polysaccharides suggests that the gel matrix neutralizes elastic deformations and lethal cell volumetric fluctuations during freezing, thus preventing the loss of homeostasis and increasing post-thaw viability. Ultimately, structured gels capable of attenuated supercooling enable cryoprotective action at the polymer-cell interface, in addition to polymer-ice interactions. This rationale potentiates implementing alternative, biobased, noncytotoxic polymers in cryobiology.

Effect of antifreeze protein I in the freezing solution on in vivo-derived sheep embryos

This study evaluated the effects of different antifreeze protein type I (AFP I) concentrations added to a slow freezing solution in sheep in vivo-derived embryos. Good-quality embryos were allocated into: AFP-free (CONT); 0.1 μg/mL of AFP I (AFP0.1); or 0.5 μg/mL of AFP I (AFP0.5). After thawing, embryos were in vitro cultured (IVC) for 48 h. At 24 h and 48 h of IVC, dead cells and apoptosis, mitochondrial activity, intracellular reactive oxygen species (ROS), and glutathione (GSH) evaluations were performed. At 24 h, evaluated embryos were submitted to RT-qPCR for metabolism (SIRT2, PRDX1, OCT4, CDX2) and quality (AQP3, CDH1, HSP70, BAX, BCL2) genes. The in vitro survival rate was 56% (22/39) for CONT, 60% (32/53) for AFP0.1, and 53% (23/43) for AFP0.5 (p > 0.05). A tendency (p = 0.09) for a higher blastocyst hatching rate was noted in AFP0.1 (62%) compared to AFP0.5 (33%), and both groups were similar to CONT (50%). An increased (p < 0.05) mitochondrial activity at 24 h was observed in AFP0.1 compared to CONT. No differences (p > 0.05) were observed in oxidative stress homeostasis and viability between treatments. A downregulation (p < 0.05) of CDH1 in AFP0.1 and a downregulation of AQP3 in AFP0.5 were observed in comparison to the other groups. An upregulation (p < 0.05) was detected in HSP70 and BCL2 on AFP0.5 compared to AFP0.1 group. The addition of AFP I in slow freezing solution can benefit cryopreserved sheep in vivo-derived embryos, without affecting embryonic survival.

Comparison of liquid nitrogen-free slow freezing protocols toward enabling a practical option for centralized cryobanking of ovarian tissue

Geographically distributed ovarian tissue cryobanks remain limited due to the high facility and staff costs, and cold transportation to centers is associated with ischemia-induced tissue damage that increases with transport distance. It is ideal to perform the cryopreservation procedure at a tissue removal site or local hospital before shipment to cost-effective centralized cryobanks. However, conventional liquid nitrogen-based freezers are not portable and require expensive infrastructure. To study the possibility of an ovarian tissue cryopreservation network not dependent on liquid nitrogen, we cryopreserved bovine ovarian tissue using three cooling techniques: a controlled rate freezer using liquid nitrogen, a liquid nitrogen-free controlled rate freezer, and liquid nitrogen-free passive cooling. Upon thawing, we evaluated a panel of viability metrics in frozen and fresh groups to examine the potency of the portable liquid nitrogen-free controlled and uncontrolled rate freezers in preserving the ovarian tissue compared to the non-portable conventional controlled rate freezer. We found similar outcomes for reactive oxygen species (ROS), total antioxidant capacity (TAC), follicular morphology, tissue viability, and fibrosis in the controlled rate freezer groups. However, passive slow cooling was associated with the lowest tissue viability, follicle morphology, and TAC, and the highest tissue fibrosis and ROS levels compared to all other groups. A stronger correlation was found between follicle morphology, ovarian tissue viability, and fibrosis with the TAC/ROS ratio compared to ROS and TAC alone. The current study undergirds the possibility of centralized cryobanks using a controlled rate liquid nitrogen-free freezer to prevent ischemia-induced damage during ovarian tissue shipment.

The association of resveratrol and AFPI did not enhance the cryoresistance of ram sperm

Cryoprotectants are required to reduce damage caused to the cells due to low temperatures during the cryopreservation. Antifreeze proteins (AFP) have a well-known role in cell membrane protection, while resveratrol is a potent antioxidant. This study assessed the effect of the association of resveratrol concentrations and AFP I in a ram semen extender. Pooled semen of four rams was allocated into six treatments in a factorial arrangement: (CONT, only the semen extender); only AFP I (ANT: 0.1 µg/mL of AFP I), only resveratrol, one treatment with two levels (10 µM/mL or 50 µM/mL of resveratrol); and two treatments with the interactions, with one AFP I and one of the two levels of resveratrol (0.1 µg/mL of AFP I with 10 µM/mL resveratrol; 0.1 µg/mL of AFP I with 50 µM/mL resveratrol). No interaction between factors was observed on sperm kinetics, plasma membrane integrity, hypo-osmotic test, and mitochondrial activity parameters. There was a high probability (P = 0.06) of reducing sperm cells with functional membrane percentage in the hypo-osmotic test and increasing the percentage of sperm with high mitochondrial activity (P = 0.07) was observed in AFP presence. An interaction of AFP and resveratrol was observed in non-capacitated sperm (P = 0.009), acrosomal reaction (P = 0.034), and sperm binding (P = 0.04). In conclusion, the association of resveratrol and AFP did not improve the quality of frozen-thawed semen and even promoted deleterious effects compared to their single addition in the semen extender. The supplementation of 50 µM/mL of resveratrol improved the outcomes of frozen-thawed ram sperm, being a potential cryoprotectant.

Engineered ice-binding protein (FfIBP) shows increased stability and resistance to thermal and chemical denaturation compared to the wildtype

Many polar organisms produce antifreeze proteins (AFPs) and ice-binding proteins (IBPs) to protect themselves from ice formation. As IBPs protect cells and organisms, the potential of IBPs as natural or biological cryoprotective agents (CPAs) for the cryopreservation of animal cells, such as oocytes and sperm, has been explored to increase the recovery rate after freezing-thawing. However, only a few IBPs have shown success in cryopreservation, possibly because of the presence of protein denaturants, such as dimethyl sulfoxide, alcohols, or ethylene glycol, in freezing buffer conditions, rendering the IBPs inactive. Therefore, we investigated the thermal and chemical stability of FfIBP isolated from Antarctic bacteria to assess its suitability as a protein-based impermeable cryoprotectant. A molecular dynamics (MD) simulation identified and generated stability-enhanced mutants (FfIBP_CC1). The results indicated that FfIBP_CC1 displayed enhanced resistance to denaturation at elevated temperatures and chemical concentrations, compared to wildtype FfIBP, and was functional in known CPAs while retaining ice-binding properties. Given that FfIBP shares an overall structure similar to DUF3494 IBPs, which are recognized as the most widespread IBP family, these findings provide important structural information on thermal and chemical stability, which could potentially be applied to other DUF3494 IBPs for future protein engineering.

Novel Apoplastic Antifreeze Proteins of Deschampsia antarctica as Enhancer of Common Cell Freezing Media for Cryobanking of Genetic Resources, a Preliminary Study

Antifreeze proteins (AFPs) are natural biomolecules found in cold-adapted organisms that lower the freezing point of water, allowing survival in icy conditions. These proteins have the potential to improve cryopreservation techniques by enhancing the quality of genetic material postthaw. Deschampsia antarctica, a freezing-tolerant plant, possesses AFPs and is a promising candidate for cryopreservation applications. In this study, we investigated the cryoprotective properties of AFPs from D. antarctica extracts on Atlantic salmon spermatozoa. Apoplastic extracts were used to determine ice recrystallization inhibition (IRI), thermal hysteresis (TH) activities and ice crystal morphology. Spermatozoa were cryopreserved using a standard cryoprotectant medium (C+) and three alternative media supplemented with apoplastic extracts. Flow cytometry was employed to measure plasma membrane integrity (PMI) and mitochondrial membrane potential (MMP) postthaw. Results showed that a low concentration of AFPs (0.05 mg/mL) provided significant IRI activity. Apoplastic extracts from D. antarctica demonstrated a cryoprotective effect on salmon spermatozoa, with PMI comparable to the standard medium. Moreover, samples treated with apoplastic extracts exhibited a higher percentage of cells with high MMP. These findings represent the first and preliminary report that suggests that AFPs derived from apoplastic extracts of D. antarctica have the potential to serve as cryoprotectants and could allow the development of novel freezing media.

Accurate Prediction of Antifreeze Protein from Sequences through Natural Language Text Processing and Interpretable Machine Learning Approaches

Antifreeze proteins (AFPs) bind to growing iceplanes owing to their structural complementarity nature, thereby inhibiting the ice-crystal growth by thermal hysteresis. Classification of AFPs from sequence is a difficult task due to their low sequence similarity, and therefore, the usual sequence similarity algorithms, like Blast and PSI-Blast, are not efficient. Here, a method combining n-gram feature vectors and machine learning models to accelerate the identification of potential AFPs from sequences is proposed. All these n-gram features are extracted from the K-mer counting method. The comparative analysis reveals that, among different machine learning models, Xgboost outperforms others in predicting AFPs from sequence when penta-mers are used as a feature vector. When tested on an independent dataset, our method performed better compared to other existing ones with sensitivity of 97.50%, recall of 98.30%, and f1 score of 99.10%. Further, we used the SHAP method, which provides important insight into the functional activity of AFPs.

Self-Assembled Nanostructures of Homo-Oligopeptide as a Potent Ice Growth Inhibitor

This study reports the formation of self-assembled nanostructures with homo-oligopeptides consisting of amino acids (i.e., alanine, threonine, valine, and tyrosine), the resulting morphologies (i.e., spherical shape, layered structure, and wire structure) in aqueous solution, and their potential as ice growth inhibitors. Among the homo-oligopeptides investigated, an alanine homo-oligopeptide (n = 5) with a spherical nanostructure showed the highest ice recrystallization inhibition (IRI) activity without showing a burst ice growth property and with low ice nucleation activity. The presence of nanoscale self-assembled structures in the solution showed superior IRI activity compared to an amino acid monomer because of the higher binding affinity of structures on the growing ice crystal plane. Simulation results revealed that the presence of nanostructures induced a significant inhibition of ice growth and increased lifetime of hydrogen bonding compared with unassembled homo-oligopeptide. These results envision extraordinary performance for self-assembled nanostructures as a desirable and potent ice growth inhibitor.

The role of antifreeze genes in the tolerance of cold stress in the Nile tilapia (Oreochromis niloticus)

BACKGROUND

Tilapia is one of the most essential farmed fishes in the world. It is a tropical and subtropical freshwater fish well adapted to warm water but sensitive to cold weather. Extreme cold weather could cause severe stress and mass mortalities in tilapia. The present study was carried out to investigate the effects of cold stress on the up-regulation of antifreeze protein (AFP) genes in Nile tilapia (Oreochromis niloticus). Two treatment groups of fish were investigated (5 replicates of 15 fish for each group in fibreglass tanks/70 L each): 1) a control group; the fish were acclimated to lab conditions for two weeks and the water temperature was maintained at 25 °C during the whole experimental period with feeding on a commercial diet (30% crude protein). 2) Cold stress group; the same conditions as the control group except for the temperature. Initially, the temperature was decreased by one degree every 12 h. The fish started showing death symptoms when the water temperature reached 6-8 °C. In this stage the tissue (muscle) samples were taken from both groups. The immune response of fish exposed to cold stress was detected and characterized using Differential Display-PCR (DD-PCR).

RESULTS

The results indicated that nine different up-regulation genes were detected in the cold-stressed fish compared to the control group. These genes are Integrin-alpha-2 (ITGA-2), Gap junction gamma-1 protein-like (GJC1), WD repeat-containing protein 59 isoform X2 (WDRP59), NUAK family SNF1-like kinase, G-protein coupled receptor-176 (GPR-176), Actin cytoskeleton-regulatory complex protein pan1-like (PAN-1), Whirlin protein (WHRN), Suppressor of tumorigenicity 7 protein isoform X2 (ST7P) and ATP-binding cassette sub-family A member 1-like isoform X2 (ABCA1). The antifreeze gene type-II amplification using a specific PCR product of 600 bp, followed by cloning and sequencing analysis revealed that the identified gene is antifreeze type-II, with similarity ranging from 70 to 95%. The in-vitro transcribed gene induced an antifreeze protein with a molecular size of 22 kDa. The antifreeze gene, ITGA-2 and the WD repeat protein belong to the lectin family (sugar-protein).

CONCLUSIONS

In conclusion, under cold stress, Nile tilapia express many defence genes, an antifreeze gene consisting of one open reading frame of approximately 0.6 kbp.

Improving cold-adaptability of mesophilic cellulase complex with a novel mushroom cellobiohydrolase for efficient low-temperature ensiling

Low ambient temperature poses a challenge for rice straw-silage processing in cold climate regions, as cold limits enzyme and microbial activity in silages. Here, a novel cold-active cellobiohydrolase (VvCBHI-I) was isolated from Volvariella volvacea, which exhibited outstanding cellobiohydrolase activity at 10-30 °C. The crude cellulase complex in the VvCBHI-I-expressing transformant T1 retained 50% relative activity at 10 °C, while the wildtype Trichoderma reesei showed <5% of the activity. VvCBHI-I greatly improved the saccharification efficiency of the cellulase complex with pretreated rice straw as substrate at 10 °C. In rice straw silage, pH (<4.5) and lactic acid content (>4.6%) remained stable after 15-day ensiling with the cellulase complex from T1 and Lactobacillus plantarum. Moreover, the proportions of cellulose and hemicellulose decreased to 29.84% ± 0.15% and 21.25% ± 0.26% of the dried material. This demonstrates the crucial potential of mushroom-derived cold-active cellobiohydrolases in successful ensiling in cold regions.

Effect of the addition of antifreeze protein type I on the quality of post-thawed domestic cat epididymal sperm

Cryopreservation of domestic cat semen is mainly performed as a model for the establishment of endangered wild feline protocols. The supplementation of antifreeze protein type I (AFP I) to cryopreservation medium has shown improvement in frozen-thawed sperm quality in other species, but its effect on cat semen has not yet been tested. This study aimed to assess the addition of AFP I to cryopreservation medium in domestic cats. Sperm was obtained from the cauda epididymis of orchiectomized cats; sperm was then pooled in Tris buffer and allocated into three treatments, according to AFP I final concentration: 0 (control), 0.1, and 0.5 µg/ml. Nine replicates were cryopreserved in a two-step protocol and subsequently thawed at 37°C for 30 s. There was no difference (P > 0.05) among the control, 0.1 and 0.5 µg/ml groups for parameters such as motility, vitality, functional membrane integrity, mature chromatin, normal morphology, and sperm binding to egg perivitelline membrane. In the 0.5 μg/ml group only, percentages of live sperm with intact acrosome and of sperm with most inactive mitochondria (DAB III) showed a significant reduction, along with a tendency (P = 0.053) to an increase in the percentage of sperm with most active mitochondria (DAB II). In conclusion, the supplementation of 0.1 and 0.5 µg/ml of AFP I did not promote consistent beneficial effects on the overall sperm cryotolerance in domestic cats.

Oxidative Stress and DNA Fragmentation in Frozen/Thawed Common Carp Cyprinus carpio Sperm With and Without Supplemental Proteins

Using cryopreservation techniques can increase the effectiveness of reproducing cultured fish species by ensuring a dependable supply of sperm, although the quality of the sperm could be impacted by the procedures involved. The goal of this study was to investigate the effect of purified seminal plasma transferrin (Tf), bovine serum albumin (BSA), and antifreeze protein (AFP) types I and III at 1 µg mL^-1 on relevant characteristics of cryopreserved sperm from common carp Cyprinus carpio. We compared oxidative stress indices, antioxidant activity, and DNA fragmentation of fresh sperm to that frozen with extender only or with Tf, BSA, or AFP types I and III. Fresh sperm had significantly lower levels of thiobarbituric acid reactive substances (TBARS) compared to samples that underwent cryopreservation without protein treatment, which resulted in 0.54 ± 0.06 nmol/10⁸ cells of TBARS. Carbonyl derivatives of proteins (CP) decreased significantly (ANOVA; P > 0.05) in carp sperm with addition of Tf, AFPI, and AFPIII. Significant differences in superoxide dismutase (SOD), glutathione reductase (GR), and glutathione peroxidase (GPx) activity were seen in sperm supplemented with Tf, BSA, AFPI, and AFPIII from those without. Significantly less DNA damage, expressed as percent tail DNA (11.56 ± 1.34) and olive tail moment (0.59 ± 0.13), was recorded in samples cryopreserved with Tf. The findings indicated that addition of Tf, BSA, AFPI, or AFPIII to cryopreservation medium is beneficial to sperm preservation. The mechanisms through which these proteins act positively on sperm need to be further investigated.

Biomedical applications of solid-binding peptides and proteins

Over the past decades, solid-binding peptides (SBPs) have found multiple applications in materials science. In non-covalent surface modification strategies, solid-binding peptides are a simple and versatile tool for the immobilization of biomolecules on a vast variety of solid surfaces. Especially in physiological environments, SBPs can increase the biocompatibility of hybrid materials and offer tunable properties for the display of biomolecules with minimal impact on their functionality. All these features make SBPs attractive for the manufacturing of bioinspired materials in diagnostic and therapeutic applications. In particular, biomedical applications such as drug delivery, biosensing, and regenerative therapies have benefited from the introduction of SBPs. Here, we review recent literature on the use of solid-binding peptides and solid-binding proteins in biomedical applications. We focus on applications where modulating the interactions between solid materials and biomolecules is crucial. In this review, we describe solid-binding peptides and proteins, providing background on sequence design and binding mechanism. We then discuss their application on materials relevant for biomedicine (calcium phosphates, silicates, ice crystals, metals, plastics, and graphene). Although the limited characterization of SBPs still represents a challenge for their design and widespread application, our review shows that SBP-mediated bioconjugation can be easily introduced into complex designs and on nanomaterials with very different surface chemistries.

Use of cryoprotectors and antioxidants in sturgeon semen cryopreservation

In recent years, the possibility of increasing the low cryoresistance of sturgeon sperm by using antioxidants in basic cryoprotective media has been studied. The goal of this work was to review the current literature on impact of the cryoprotectors, well-known antioxidants and new multifunctional compounds on the activity indicators and fertilizing capability of sperm, as well as on biomarkers of cryostress. A special attention is given to the radical scavenging activity of studied compounds in relation to the highly reactive oxygen species, to prevent and negate oxidative stress damage of sturgeon sperm. Also, new trends for future research through the application of novel polyfunctional antioxidants to sturgeon sperm cryopreservation were indicated.

Effects of Antifreeze Protein Type I and Glycerol in Diluents on Cryopreserved Goat Epididymal Sperm

The effect of antifreeze protein (AFP) as a cryoprotectant used in different concentrations of glycerol on post-thaw quality of epididymal sperm was investigated. Sperm were isolated from 50 testicles, obtained from 25 healthy mature goat bucks, with progressive motility >80%, and total morphological abnormalities <10% were pooled in each replication. The semen samples were diluted with Tris-citrate-fructose-soybean lecithin extender containing different concentration of AFP [0 μg/mL (A0), 5 μg/mL (A5), 10 μg/mL (A10)]. Each concentration of AFP was added in an extender containing either 7% (G7) or 5% (G5) glycerol. Post-thaw total and progressive motility were found to be higher (p < 0.05) in groups A5G5 and A5G7. Plasma membrane integrity, sperm acrosome integrity, DNA integrity, acrosome intact sperm, and mitochondrial membrane potential were found to be higher (p < 0.05) in groups A5G5 and A10G5. Sperm viability was found to be higher (p < 0.05) in group A5G5, while lipid peroxidation was recorded lower (p < 0.05) in groups A5G5 and A5G7. Regarding the apoptosis occurrence, the results demonstrate higher (p < 0.05) live post-thawed spermatozoa for groups containing 5 μg/mL AFP with 5% and 7% glycerol in addition to the lowest (p < 0.05) value for groups containing 0 μg/mL AFP with 5% and 7% glycerol. Based on these results, the present study concludes that the addition of 5 μg/mL AFP in combination with 5% glycerol in freezing extender improves the post-thaw quality, structure, and function parameters for buck spermatozoa.

Nanoscopy of single antifreeze proteins reveals that reversible ice binding is sufficient for ice recrystallization inhibition but not thermal hysteresis

Antifreeze proteins (AFPs) bind ice to reduce freezing temperatures and arrest ice crystal ripening, making AFPs essential for the survival of many organisms in ice-laden environments and attractive as biocompatible antifreezes in many applications. While their activity was identified over 50 years ago, the physical mechanisms through which they function are still debated because experimental insights at the molecular scale remain elusive. Here, we introduce subzero nanoscopy by the design and incorporation of a freezing stage on a commercial super-resolution setup to resolve the interfacial dynamics of single AFPs with ice crystal surfaces. Using this method, we demonstrate irreversible binding and immobilization (i.e., pinning) of individual proteins to the ice/water interface. Surprisingly, pinning is lost and adsorption becomes reversible when freezing point depression activity, but not ice recrystallization inhibition, is eliminated by a single mutation in the ice-binding site of the AFP. Our results provide direct experimental evidence for the adsorption-inhibition paradigm, pivotal to all theoretical descriptions of freezing point depression activity, but also reveal that reversible binding to ice must be accounted for in an all-inclusive model for AFP activity. These mechanistic insights into the relation between interfacial interactions and activity further our understanding and may serve as leading principles in the future design of highly potent, biocompatible antifreezes with tunable affinity.

Polysaccharide-Derived Ice Recrystallization Inhibitors with a Modular Design: The Case of Dextran-Based Graft Polymers

Ice recrystallization inhibitors inspired from antifreeze proteins (AFPs) are receiving increasing interest for cryobiology and other extreme environment applications. Here, we present a modular strategy to develop polysaccharide-derived biomimetics, and detailed studies were performed in the case of dextran. Poly(vinyl alcohol) (PVA) which has been termed as one of the most potent biomimetics of AFPs was grafted onto dextran via thiol-ene click chemistry (Dex-g-PVA). This demonstrated that Dex-g-PVA is effective in IRI and its activity increases with the degree of polymerization (DP) (sizes of ice crystals were 18.846 ± 1.759 and 9.700 ± 1.920 μm with DPs of 30 and 80, respectively) and fraction of PVA. By means of the dynamic ice shaping (DIS) assay, Dex-g-PVA is found to engage on the ice crystal surfaces, thus the ice affinity accounts for their IRI activity. In addition, Dex- g-PVA displayed enhanced IRI activity compared to that of equivalent PVA alone. We speculate that the hydrophilic nature of dextran would derive PVA in a stretch conformation that favors ice binding. The modular design can not only offer polysaccharides IRI activity but also favor the ice-binding behavior of PVA.

Peptide-DNA origami as a cryoprotectant for cell preservation

Cryopreservation of cells is essential for the conservation and cold chain of bioproducts and cell-based medicines. Here, we demonstrate that self-assembled DNA origami nanostructures have a substantial ability to protect cells undergoing freeze-thaw cycles; thereby, they can be used as cryoprotectant agents, because their nanoscale morphology and ice-philicity are tailored. In particular, a single-layered DNA origami nanopatch functionalized with antifreezing threonine peptides enabled the viability of HSC-3 cells to reach 56% after 1 month of cryopreservation, surpassing dimethyl sulfoxide, which produced 38% viability. It also exhibited minimal dependence on the cryopreservation period and freezing conditions. We attribute this outcome to the fact that the peptide-functionalized DNA nanopatches exert multisite actions for the retardation of ice growth in both intra- and extracellular regions and the protection of cell membranes during cryopreservation. This discovery is expected to deepen our fundamental understanding of cell survival under freezing environment and affect current cryopreservation technologies.

Application of Nanoparticles and Melatonin for Cryopreservation of Gametes and Embryos

Cryopreservation of gametes and embryos, a technique widely applied in human infertility clinics and to preserve desirable genetic traits of livestock, has been developed over 30 years as a component of the artificial insemination process. A number of researchers have conducted studies to reduce cell toxicity during cryopreservation using adjuvants leading to higher gamete and embryo survival rates. Melatonin and Nanoparticles are novel cryoprotectants and recent studies have investigated their properties such as regulating oxidative stresses, lipid peroxidation, and DNA fragmentation in order to protect gametes and embryos during vitrification. This review presented the current status of cryoprotectants and highlights the novel biomaterials such as melatonin and nanoparticles that may improve the survivability of gametes and embryos during this process.

Cold-inducible promoter-driven knockdown of Brachypodium antifreeze proteins confers freezing and phytopathogen susceptibility

The model forage crop, Brachypodium distachyon, has a cluster of ice recrystallization inhibition (BdIRI) genes, which encode antifreeze proteins that function by adsorbing to ice crystals and inhibiting their growth. The genes were targeted for knockdown using a cold-induced promoter from rice (prOsMYB1R35) to drive miRNA. The transgenic lines showed no apparent pleiotropic developmental defects but had reduced antifreeze activity as assessed by assays for ice-recrystallization inhibition, thermal hysteresis, electrolyte leakage, and leaf infrared thermography. Strikingly, the number of cold-acclimated transgenic plants that survived freezing at -8°C was reduced by half or killed entirely, depending on the line, compared with cold-acclimated wild type plants. In addition, more leaf damage was apparent at subzero temperatures in knockdowns after infection with an ice nucleating pathogen, Pseudomonas syringae. Although antifreeze proteins have been studied for almost 60 years, this is the first unequivocal demonstration of their function by knockdown in any organism, and their dual contribution to freeze protection as well as pathogen susceptibility, independent of obvious developmental defects. These proteins are thus of potential interest in a wide range of biotechnological applications from cryopreservation, to frozen product additives, to the engineering of transgenic crops with enhanced pathogen and freezing tolerance.

Therapeutic Potential of Marine Bioactive Peptides against Human Immunodeficiency Virus: Recent Evidence, Challenges, and Future Trends

Acquired immunodeficiency syndrome (AIDS) is a chronic and potentially fatal ailment caused by the human immunodeficiency virus (HIV) and remains a major health problem worldwide. In recent years, the research focus has shifted to a greater emphasis on complementing treatment regimens involving conventional antiretroviral (ARV) drug therapies with novel lead structures isolated from various marine organisms that have the potential to be utilized as therapeutics for the management of HIV-AIDS. The present review summarizes the recent developments regarding bioactive peptides sourced from various marine organisms. This includes a discussion encompassing the potential of these novel marine bioactive peptides with regard to antiretroviral activities against HIV, preparation, purification, and processing techniques, in addition to insight into the future trends with an emphasis on the potential of exploration and evaluation of novel peptides to be developed into effective antiretroviral drugs.

RhoA improves cryopreservation of rooster sperm through the Rho/RhoA-associated Kinase/cofilin pathway

Cryopreservation of rooster sperm leads to relatively low semen quality due to cytoskeletal damage during the freeze-thawing process. This study aimed to explore how the addition of RhoA recombinant protein affected the viability and subcellular structure of rooster sperm after freeze-thawing and elucidated the molecular mechanisms of sperm cryopreservation. Semen quality and acrosome integrity testing revealed that the addition of 0.5 μg/mL RhoA recombinant protein to the cryoprotectant fluid significantly increased sperm motility, survival rate, linearity, straight-line velocity, and acrosome integrity after freeze-thawing (P < 0.05). Ultrastructure analysis of cryopreserved sperm showed structural damage to the sperm plasma membrane, nuclear membrane, and tail. However, compared to the control, these structural changes were reduced upon the addition of RhoA recombinant protein to the cryoprotective fluid (P < 0.05). Western blotting revealed that the expression of Rho/RhoA-associated kinase and p-cofilin was increased, and cofilin expression was decreased after sperm cryopreservation with recombinant RhoA protein. Treatment with Y-27632, a ROCK antagonist, suppressed ROCK and p-cofilin expression and decreased semen quality, acrosome integrity, and ultrastructure integrity. In summary, we have demonstrated a cryoprotective effect in spermatozoa involving the Rho/ROCK pathway during freeze-thawing. Furthermore, the addition of 0.5 μg/mL RhoA recombinant protein to the cryoprotective fluid improved rooster semen quality and subcellular structural homeostasis after freeze-thawing via the Rho/ROCK pathway. This pathway may regulate the dynamic reorganization of the actin cytoskeleton by regulating the cofilin phosphorylation.

Exopolysaccharide ID1 Improves Post-Warming Outcomes after Vitrification of In Vitro-Produced Bovine Embryos

This study aimed to assess the cryoprotectant role of exopolysaccharide (EPS) ID1, produced by Antarctic Pseudomonas sp., in the vitrification of in vitro-produced (IVP) bovine embryos. IVP day 7 (D7) and day 8 (D8) expanded blastocysts derived from cow or calf oocytes were vitrified without supplementation (EPS0) or supplemented with 10 µg/mL (EPS10) or 100 µg/mL (EPS100) EPS ID1. The effect of EPS ID1 was assessed in post-warming re-expansion and hatching rates, differential cell count, apoptosis rate, and gene expression. EPS100 re-expansion rates were significantly higher than those observed for the EPS0 and EPS10 treatments, regardless of culture length or oocyte source. EPS100 hatching rate was similar to the one of the fresh blastocysts except for those D7 blastocysts derived from calf oocytes. No differences were observed among EPS ID1 treatments when the inner cell mass, trophectoderm, and total cell number were assessed. Although apoptosis rates were higher (p ≤ 0.05) in vitrified groups compared to fresh embryos, EPS100 blastocysts had a lower number (p ≤ 0.05) of apoptotic nuclei than the EPS0 or EPS10 groups. No differences in the expression of BCL2, AQP3, CX43, and SOD1 genes between treatments were observed. Vitrification without EPS ID1 supplementation produced blastocysts with significantly higher BAX gene expression, whereas treatment with 100 µg/mL EPS ID1 returned BAX levels to those observed in non-vitrified blastocysts. Our results suggest that 100 µg/mL EPS ID1 added to the vitrification media is beneficial for embryo cryopreservation because it results in higher re-expansion and hatching ability and it positively modulates apoptosis.

Origin of an antifreeze protein gene in response to Cenozoic climate change

Antifreeze proteins (AFPs) inhibit ice growth within fish and protect them from freezing in icy seawater. Alanine-rich, alpha-helical AFPs (type I) have independently (convergently) evolved in four branches of fishes, one of which is a subsection of the righteye flounders. The origin of this gene family has been elucidated by sequencing two loci from a starry flounder, Platichthys stellatus, collected off Vancouver Island, British Columbia. The first locus had two alleles that demonstrated the plasticity of the AFP gene family, one encoding 33 AFPs and the other allele only four. In the closely related Pacific halibut, this locus encodes multiple Gig2 (antiviral) proteins, but in the starry flounder, the Gig2 genes were found at a second locus due to a lineage-specific duplication event. An ancestral Gig2 gave rise to a 3-kDa "skin" AFP isoform, encoding three Ala-rich 11-a.a. repeats, that is expressed in skin and other peripheral tissues. Subsequent gene duplications, followed by internal duplications of the 11 a.a. repeat and the gain of a signal sequence, gave rise to circulating AFP isoforms. One of these, the "hyperactive" 32-kDa Maxi likely underwent a contraction to a shorter 3.3-kDa "liver" isoform. Present day starry flounders found in Pacific Rim coastal waters from California to Alaska show a positive correlation between latitude and AFP gene dosage, with the shorter allele being more prevalent at lower latitudes. This study conclusively demonstrates that the flounder AFP arose from the Gig2 gene, so it is evolutionarily unrelated to the three other classes of type I AFPs from non-flounders. Additionally, this gene arose and underwent amplification coincident with the onset of ocean cooling during the Cenozoic ice ages.

Intracellular and Extracellular Antifreeze Protein Significantly Improves Mammalian Cell Cryopreservation

Cell cryopreservation is an essential part of the biotechnology, food, and health care industries. There is a need to develop more effective, less toxic cryoprotective agents (CPAs) and methods, especially for mammalian cells. We investigated the impact of an insect antifreeze protein from Anatolica polita (ApAFP752) on mammalian cell cryopreservation using the human embryonic kidney cell line HEK 293T. An enhanced green fluorescent protein (EGFP)-tagged antifreeze protein, EGFP-ApAFP752, was transfected into the cells and the GFP was used to determine the efficiency of transfection. AFP was assessed for its cryoprotective effects intra- and extracellularly and both simultaneously at different concentrations with and without dimethyl sulfoxide (DMSO) at different concentrations. Comparisons were made to DMSO or medium alone. Cells were cryopreserved at -196 °C for ≥4 weeks. Upon thawing, cellular viability was determined using trypan blue, cellular damage was assessed by lactate dehydrogenase (LDH) assay, and cellular metabolism was measured using a metabolic activity assay (MTS). The use of this AFP significantly improved cryopreserved cell survival when used with DMSO intracellularly. Extracellular AFP also significantly improved cell survival when included in the DMSO freezing medium. Intra- and extracellular AFP used together demonstrated the most significantly increased cryoprotection compared to DMSO alone. These findings present a potential method to improve the viability of cryopreserved mammalian cells.

Ice crystal recrystallization inhibition of type I antifreeze protein, type III antifreeze protein, and antifreeze glycoprotein: effects of AF(G)Ps concentration and heat treatment

This study compared ice recrystallization behaviors of frozen dessert model systems containing type I antifreeze protein (AFP I), type III antifreeze protein (AFP III), and antifreeze glycoprotein (AFGP) at -10 °C. Specifically, effects of AF(G)P concentration and heat treatment (95 °C for 10 min) were examined. The concentration dependence of the ice recrystallization rate constant reasonably well fit a sigmoidal function: the fitting procedure was proposed, along with cooperative coefficient α, and a new index of AF(G)P ice recrystallization inhibition (IRI) activity (C50). After 95 °C heat treatment for 10 min, AFP III lost its ice crystal recrystallization inhibitory activity the most: AFP I was less affected; AFGP was almost entirely unaffected. These different thermal treatment effects might reflect a lower degree of protein aggregation because of hydrophobic interaction after heat treatment or might reflect the simplicity and flexibility of the higher order structures of AFP I and AFGP.

Bioinspired Ice-Binding Materials for Tissue and Organ Cryopreservation

Cryopreservation of tissues and organs can bring transformative changes to medicine and medical science. In the past decades, limited progress has been achieved, although cryopreservation of tissues and organs has long been intensively pursued. One key reason is that the cryoprotective agents (CPAs) currently used for cell cryopreservation cannot effectively preserve tissues and organs because of their cytotoxicity and tissue destructive effect as well as the low efficiency in controlling ice formation. In stark contrast, nature has its unique ways of controlling ice formation, and many living organisms can effectively prevent freezing damage. Ice-binding proteins (IBPs) are regarded as the essential materials identified in these living organisms for regulating ice nucleation and growth. Note that controversial results have been reported on the utilization of IBPs and their mimics for the cryopreservation of tissues and organs, that is, some groups revealed that IBPs and mimics exhibited unique superiorities in tissues cryopreservation, while other groups showed detrimental effects. In this perspective, we analyze possible reasons for the controversy and predict future research directions in the design and construction of IBP inspired ice-binding materials to be used as new CPAs for tissue cryopreservation after briefly introducing the cryo-injuries and the challenges of conventional CPAs in the cryopreservation of tissues and organs.

Importance of rigidity of ice-binding protein (FfIBP) for hyperthermal hysteresis activity and microbial survival

Ice-binding proteins (IBPs) are well-characterized proteins responsible for the cold-adaptation mechanisms. Despite extensive structural and biological investigation of IBPs and antifreeze proteins, only a few studies have considered the relationship between protein stabilization and thermal hysteresis (TH) activity as well as the implication of hyperactivity. Here, we investigated the important role of the head capping region in stabilization and the hyper-TH activity of FfIBP using molecular dynamics simulation. Data comparison revealed that residues on the ice-binding site of the hyperactive FfIBP are immobilized, which could be correlated with TH activity. Further comparison analysis indicated the disulfide bond in the head region is mainly involved in protein stabilization and is crucial for hyper-TH activity. This finding could also be generalized to known hyperactive IBPs. Furthermore, in mimicking the physiological conditions, bacteria with membrane-anchored FfIBP formed brine pockets in a TH activity-dependent manner. Cells with a higher number of TH-active IBPs showed an increased number of brine pockets, which may be beneficial for short- and long-term survival in cold environments by reducing the salt concentration. The newly identified conditions for hyper-TH activity and their implications on bacterial survival provide insights into novel mechanistic aspects of cold adaptation in polar microorganisms.

Antifreeze Proteins: A Tale of Evolution From Origin to Energy Applications

Icing and formation of ice crystals is a major obstacle against applications ranging from energy systems to transportation and aviation. Icing not only introduces excess thermal resistance, but it also reduces the safety in operating systems. Many organisms living under harsh climate and subzero temperature conditions have developed extraordinary survival strategies to avoid or delay ice crystal formation. There are several types of antifreeze glycoproteins with ice-binding ability to hamper ice growth, ice nucleation, and recrystallization. Scientists adopted similar approaches to utilize a new generation of engineered antifreeze and ice-binding proteins as bio cryoprotective agents for preservation and industrial applications. There are numerous types of antifreeze proteins (AFPs) categorized according to their structures and functions. The main challenge in employing such biomolecules on industrial surfaces is the stabilization/coating with high efficiency. In this review, we discuss various classes of antifreeze proteins. Our particular focus is on the elaboration of potential industrial applications of anti-freeze polypeptides.

Antifreeze proteins and their biomimetics for cell cryopreservation: Mechanism, function and application-A review

Cell-based therapy is a promising technology for intractable diseases and health care applications, in which cryopreservation has become an essential procedure to realize the production of therapeutic cells. Ice recrystallization is the major factor that affects the post-thaw viability of cells. As a typical series of biomacromolecules with ice recrystallization inhibition (IRI) activity, antifreeze proteins (AFPs) have been employed in cell cryopreservation. Meanwhile, synthesized materials with IRI activity have emerged in the name of biomimetics of AFPs to expand their availability and practicality. However, fabrication of AFPs mimetics is in a chaotic period. There remains little commonality among different AFPs mimetics, then it is difficult to set guidelines on their design. With no doubt, a comprehensive understanding on the antifreezing mechanism of AFPs in molecular level will enable us to rebuild the function of AFPs, and provide convenience to clarify the relationship between structure and function of these early stage biomimetics. In this review, we would discuss those previously reported biomimetics to summarize their structure characteristics concerning the IRI activity and attempt to develop a roadmap for guiding the design of novel AFPs mimetics.

The role of trifunctional cryoprotectants in the frozen storage of aquatic foods: Recent developments and future recommendations

Freeze-induced changes including protein denaturation, ice crystals formation and lipid oxidation are mainly responsible for the quality deterioration persistent in aquatic foods. Here, for the first time, the cryoprotectants with trifunctional properties have been suggested for aquatic food cryopreservation and have exhibited exceptional cryoprotective abilities. In this study, in-depth discussion of protein denaturation, ice crystal formation and lipid oxidation is added in order to understand their mechanism, emphasizing on the necessity and use of trifunctional cryoprotectants in aquatic foods during frozen storage. Trifunctional cryoprotectants have strong abilities to prevent the formation of malondihaldehyde and aldehydes resulting from lipid oxidation, which further interact with proteins, subsequently lead to protein denaturation. Besides these all cryoprotective properties, ice crystal binding abilities distinguish trifunctional cryoprotectants from conventional cryoprotectants. Moreover, this study added with recent advances in cryoprotectants including antifreeze proteins and protein hydrolysates with their role in retarded freeze-induced changes. This study concluded that trifunctional cryoprotectants are effective owing to their hydrophilic amino acid chains, radical scavenging, water entrapping abilities, as well as the hydroxyl groups, which interact at the functional sites of protein molecules. Furthermore, polysaccharides and protein hydrolysates are the potential ingredients with trifunctional cryoproperties. However, more scientific research is required for material optimization to attain the desired level of cryoprotection.

Anti freeze proteins (Afp): Properties, sources and applications - A review

Extreme cold marine and freshwater temperatures (below 4 °C) induce massive deterioration to the cell membranes of organisms resulting in the formation of ice crystals, consequently causing organelle damage or cell death. One of the adaptive mechanisms organisms have evolved to thrive in cold environments is the production of antifreeze proteins with the functional capabilities to withstand frigid temperatures. Antifreeze proteins are extensively identified in different cold-tolerant species and they facilitate the persistence of cold-adapted organisms by decreasing the freezing point of their body fluids. Various structurally diverse types of antifreeze proteins detected possess the ability to modify ice crystal growth by thermal hysteresis and ice recrystallization inhibition. The unique properties of antifreeze proteins have made them a promising resource in industry, biomedicine, food storage and cryobiology. This review collates the findings of the various studies carried out in the past and the recent developments observed in the properties, functional mechanisms, classification, distinct sources and the ever-increasing applications of antifreeze proteins. This review also summarizes the possibilities of the way forward to identify new avenues of research on anti-freeze proteins.

Improving Sperm Cryopreservation With Type III Antifreeze Protein: Proteomic Profiling of Cynomolgus Macaque (Macaca fascicularis) Sperm

Antifreeze protein III (AFP III) is used for the cryopreservation of germ cells in various animal species. However, the exact mechanism of its cryoprotection is largely unknown at the molecular level. In this study, we investigated the motility, acrosomal integrity, and mitochondrial membrane potential (MMP), as well as proteomic change, of cynomolgus macaque sperm after cryopreservation. Sperm motility, acrosomal integrity, and MMP were lower after cryopreservation (p < 0.001), but significant differences in sperm motility and MMP were observed between the AFP-treated sperm sample (Cryo+AFP) and the non-treated sample (Cryo–AFP) (p < 0.01). A total of 141 and 32 differentially expressed proteins were, respectively, identified in cynomolgus macaque sperm cryopreserved without and with 0.1 μg/ml AFP III compared with fresh sperm. These proteins were mainly involved in the mitochondrial production of reactive oxygen species (ROS), glutathione (GSH) synthesis, and cell apoptosis. The addition of AFP III in the sperm freezing medium resulted in significant stabilization of cellular molecular functions and/or biological processes in sperm, as illustrated by the extent of proteomic changes after freezing and thawing. According to the proteomic change of differentially expressed proteins, we hypothesized a novel molecular mechanism for cryoprotection that AFP III may reduce the release of cytochrome c and thereby reduce sperm apoptosis by modulating the production of ROS in mitochondria. The molecular mechanism that AFP III acts with sperm proteins for cellular protection against cryoinjuries needs further study.

Cold Adaptation Strategies and the Potential of Psychrophilic Enzymes from the Antarctic Yeast, Glaciozyma antarctica PI12

Psychrophilic organisms possess several adaptive strategies which allow them to sustain life at low temperatures between −20 to 20 °C. Studies on Antarctic psychrophiles are interesting due to the multiple stressors that exist on the permanently cold continent. These organisms produce, among other peculiarities, cold-active enzymes which not only have tremendous biotechnological potential but are valuable models for fundamental research into protein structure and function. Recent innovations in omics technologies such as genomics, transcriptomics, proteomics and metabolomics have contributed a remarkable perspective of the molecular basis underpinning the mechanisms of cold adaptation. This review critically discusses similar and different strategies of cold adaptation in the obligate psychrophilic yeast, Glaciozyma antarctica PI12 at the molecular (genome structure, proteins and enzymes, gene expression) and physiological (antifreeze proteins, membrane fluidity, stress-related proteins) levels. Our extensive studies on G. antarctica have revealed significant insights towards the innate capacity of- and the adaptation strategies employed by this psychrophilic yeast for life in the persistent cold. Furthermore, several cold-active enzymes and proteins with biotechnological potential are also discussed.

Antifreeze Protein Supplementation During the Warming of Vitrified Bovine Ovarian Tissue Can Improve the Ovarian Tissue Quality After Xenotransplantation

The occurrence of ice crystallization during ovarian tissue (OT) cryopreservation causes unavoidable cryodamage, and ice recrystallization during the warming is more detrimental than ice crystallization. Here, we investigated that antifreeze protein (AFP) treatment during the warming procedure can improve the bovine OT quality after xenotransplantation (XT). Bovine OTs (n=120) were evenly assigned to four groups: fresh, vitrified-warmed, vitrified-warmed with 10 mg/mL Leucosporidium ice-binding protein (LeIBP, a type of AFP) (LeIBP-10), and vitrified-warmed with 20 mg/mL LeIBP (LeiBP-20). LeIBPs were added to the first warming solution. Twenty pieces of OTs were assigned to each category. The remaining 10 OTs from each category were assigned to the XT-Fresh control, XT-Vitrified-warmed control, XT-LeIBP-10, and XT-LeIBP-20 groups, respectively, and xenotransplanted to 9-week-old ovariectomized nude mice for one week. LeIBP treatment during the warming step increased morphological follicle normality and decreased apoptotic follicle ratios after vitrification-warming and XT. The XT-vitrified-warmed control group showed significantly reduced microvessel density and increased fibrosis when compared to that of the XT-fresh group. Microvessel density and fibrosis were recovered in both LeIBP treated groups. There was no significant difference between the LeIBP-10 and LeIBP-20 groups in all outcomes. AFP treatment during the warming procedure can prevent OT damage, and improve ovarian follicle morphology and apoptosis in both the vitrified-warmed bovine OT and its graft. After confirmation in a human study, AFPs can potentially be applied to human OT cryopreservation to reduce cryodamage and improve the OT quality.

Disaccharide Residues are Required for Native Antifreeze Glycoprotein Activity

Antifreeze glycoproteins (AFGPs) are able to bind to ice, halt its growth, and are the most potent inhibitors of ice recrystallization known. The structural basis for AFGP’s unique properties remains largely elusive. Here we determined the antifreeze activities of AFGP variants that we constructed by chemically modifying the hydroxyl groups of the disaccharide of natural AFGPs. Using nuclear magnetic resonance, two-dimensional infrared spectroscopy, and circular dichroism, the expected modifications were confirmed as well as their effect on AFGPs solution structure. We find that the presence of all the hydroxyls on the disaccharides is a requirement for the native AFGP hysteresis as well as the maximal inhibition of ice recrystallization. The saccharide hydroxyls are apparently as important as the acetyl group on the galactosamine, the α-linkage between the disaccharide and threonine, and the methyl groups on the threonine and alanine. We conclude that the use of hydrogen-bonding through the hydroxyl groups of the disaccharide and hydrophobic interactions through the polypeptide backbone are equally important in promoting the antifreeze activities observed in the native AFGPs. These important criteria should be considered when designing synthetic mimics.

Effects of Antifreeze Protein III on Sperm Cryopreservation of Pacific Abalone, Haliotis discus hannai

Pacific abalone (Haliotis discus hannai) is a highly commercial seafood in Southeast Asia. The aim of the present study was to improve the sperm cryopreservation technique for this valuable species using an antifreeze protein III (AFPIII). Post-thaw sperm quality parameters including motility, acrosome integrity (AI), plasma membrane integrity (PMI), mitochondrial membrane potential (MMP), DNA integrity, fertility, hatchability, and mRNA abundance level of heat shock protein 90 (HSP90) were determined to ensure improvement of the cryopreservation technique. Post-thaw motility of sperm cryopreserved with AFPIII at 10 µg/mL combined with 8% dimethyl sulfoxide (DMSO) (61.3 ± 2.7%), 8% ethylene glycol (EG) (54.3 ± 3.3%), 6% propylene glycol (PG) (36.6 ± 2.6%), or 2% glycerol (GLY) (51.7 ± 3.0%) was significantly improved than that of sperm cryopreserved without AFPIII. Post-thaw motility of sperm cryopreserved with 2% MeOH and 1 µg/mL of AFPIII was also improved than that of sperm cryopreserved without AFPIII. A combination of 10 µg/mL AFPIII with 8% DMSO resulted in the highest post-thaw motility, showing AI of 60.1 ± 3.9%, PMI of 67.2 ± 4.0%, and MMP of 59.1 ± 4.3%. DNA integrity of sperm cryopreserved using 10 µg/mL AFPIII combined with 8% DMSO was not significantly (p > 0.05) different from that of fresh sperm. Cryopreservation using a combination of AFPIII with 8% DMSO improved fertilization and hatching rates of sperm compared to that of cryopreservation without supplementation of 10 µg/mL AFPIII. Sperm cryopreserved using AFPIII showed higher mRNA abundance levels of HSP90 than those cryopreserved without AFPIII. Results of the present study suggest that 10 µg/mL AFPIII combined with 8% DMSO can be used for large scale cryopreservation of Pacific abalone sperm and for hatchery production.

Ice Inhibition for Cryopreservation: Materials, Strategies, and Challenges

Cryopreservation technology has developed into a fundamental and important supporting method for biomedical applications such as cell-based therapeutics, tissue engineering, assisted reproduction, and vaccine storage. The formation, growth, and recrystallization of ice crystals are the major limitations in cell/tissue/organ cryopreservation, and cause fatal cryoinjury to cryopreserved biological samples. Flourishing anti-icing materials and strategies can effectively regulate and suppress ice crystals, thus reducing ice damage and promoting cryopreservation efficiency. This review first describes the basic ice cryodamage mechanisms in the cryopreservation process. The recent development of chemical ice-inhibition molecules, including cryoprotectant, antifreeze protein, synthetic polymer, nanomaterial, and hydrogel, and their applications in cryopreservation are summarized. The advanced engineering strategies, including trehalose delivery, cell encapsulation, and bioinspired structure design for ice inhibition, are further discussed. Furthermore, external physical field technologies used for inhibiting ice crystals in both the cooling and thawing processes are systematically reviewed. Finally, the current challenges and future perspectives in the field of ice inhibition for high-efficiency cryopreservation are proposed.

Cryopreservation of plant cell cultures - Diverse practices and protocols

Plant cell cultures can be used as biotechnological platforms for the commercial production of small-molecule active ingredients and recombinant proteins, such as biopharmaceuticals. This requires the cryopreservation of well-characterized cell lines as master cell banks from which uniform working cell banks can be derived to ensure high batch-to-batch reproducibility during production campaigns. However, the cryopreservation of plant cells is challenging due to their low viability and poor regrowth after thawing. Three approaches have been developed: slow freezing, vitrification, and encapsulation-dehydration. Typically, the protocols are iteratively adapted to accommodate the properties of different plant cell lines, taking time and resources while achieving moderate success. Since standardized processes are a prerequisite for industrial applications, this review presents an in-depth analysis of the different procedures for cryopreservation of plant suspension cell cultures, highlighting relevant parameters for effective cryopreservation and the re-establishment of vigorous plant cell cultures within weeks. The protocol variants are grouped into modules that facilitate the directed improvement of each step and allow protocol evolution by module recombination. Ultimately, such improved cryopreservation protocols will form the basis of processes that comply with good manufacturing practice and attract major biopharmaceutical companies to the benefits of plant molecular farming.

Molecular basis of ice-binding and cryopreservation activities of type III antifreeze proteins

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The QAE2ACT and SP ACT mutants showed full TH and IRI activities.

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Active AFPs effectively preserved intact follicle and prevented DSB damage.

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Active AFPs exhibited unique structural feature in the first 3₁₀ helix of the IBS.

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Unique structure of the IBS determines TH, IRI, and cryopreservation activities.

Antifreeze proteins (AFPs) can inhibit the freezing of body fluid at subzero temperatures to promote the survival of various organisms living in polar regions. Type III AFPs are categorized into three subgroups, QAE1, QAE2, and SP isoforms, based on differences in their isoelectric points. We determined the thermal hysteresis (TH), ice recrystallization inhibition (IRI), and cryopreservation activity of three isoforms of the notched-fin eelpout AFP and their mutant constructs and characterized their structural and dynamic features using NMR. The QAE1 isoform is the most active among the three classes of III AFP isoforms, and the mutants of inactive QAE2 and SP isoforms, QAE2^ACT and SP^ACT, displayed the full TH and IRI activities with resepect to QAE1 isoform. Cryopreservation studies using mouse ovarian tissue revealed that the QAE1 isoform and the active mutants, QAE2^ACT and SP^ACT, more effectively preserved intact follicle morphology and prevented DNA double-strand break damage more efficiently than the inactive isoforms. It was also found that all active AFPs, QAE1, QAE2^ACT, and SP^ACT, formed unique H-bonds with the first 3₁₀ helix, an interaction that plays an important role in the formation of anchored clathrate water networks for efficient binding to the primary prism and pyramidal planes of ice crystals, which was disrupted in the inactive isoforms. Our studies provide valuable insights into the molecular mechanism of the TH and IRI activity, as well as the cryopreservation efficiency, of type III AFPs.

Design and Synthesis of Mucin-Inspired Glycopolymers

Mucins are bottlebrush biopolymers that are glycoproteins on the surfaces of cells and as hydrogels secreted inside and outside the body. Mucin function in biology includes cell-cell recognition, signaling, protection, adhesion, and lubrication. Because of their attractive and diverse properties, mucins have recently become the focus of synthetic efforts by researchers who hope to understand and emulate these biomaterials. This review is focused on the development of methodologies for preparing mucin-inspired synthetic oligomers and glycopolymers, including solid-phase synthesis, polymerization of glycosylated monomers, and post-polymerization grafting of glycans to polymer chains. How these synthetic mucins have been used in health applications is discussed. Natural mucins are formed from a conserved set of monomers that are combined into chains of different sequences and lengths to achieve materials with widely diverse properties. Adopting this design paradigm from natural mucins could lead to next-generation bioinspired synthetic materials.

Protection of Alcohol Dehydrogenase against Freeze-Thaw Stress by Ice-Binding Proteins Is Proportional to Their Ice Recrystallization Inhibition Property

Ice-binding proteins (IBPs) have ice recrystallization inhibition (IRI) activity. IRI property has been extensively utilized for the cryopreservation of different types of cells and tissues. Recent reports demonstrated that IRI can also play a significant role in protecting proteins from freezing damage during freeze-thaw cycles. In this study, we hypothesized that the protective capability of IBPs on proteins against freeze-thaw damage is proportional to their IRI activity. Hence we used two IBPs: one with higher IRI activity (LeIBP) and the other with lower activity (FfIBP). Yeast alcohol dehydrogenase (ADH) was used as a freeze-labile model protein. IBPs and ADH were mixed, frozen at -20 °C, and thawed repeatedly. The structure of ADH was assessed using fluorescence emission spectra probed by 1-anilinonaphthalene-8-sulfonate over the repeated freeze-thaw cycles. The activity was monitored at 340 nm spectrophotometrically. Fluorescence data and activity clearly indicated that ADH without IBP was freeze-labile. However, ADH maintained about 70% residual activity after five repeated cycles at a minimal concentration of 0.1 mg mL^-1 of high IRI-active LeIBP, but only 50% activity at 4 mg mL^-1 of low active FfIBP. These results showed that the protection of proteins from freeze-thaw stress by IBPs is proportional to their IRI activity.

Antifreeze Proteins and Their Practical Utilization in Industry, Medicine, and Agriculture

Antifreeze proteins (AFPs) are specific proteins, glycopeptides, and peptides made by different organisms to allow cells to survive in sub-zero conditions. AFPs function by reducing the water’s freezing point and avoiding ice crystals’ growth in the frozen stage. Their capability in modifying ice growth leads to the stabilization of ice crystals within a given temperature range and the inhibition of ice recrystallization that decreases the drip loss during thawing. This review presents the potential applications of AFPs from different sources and types. AFPs can be found in diverse sources such as fish, yeast, plants, bacteria, and insects. Various sources reveal different α-helices and β-sheets structures. Recently, analysis of AFPs has been conducted through bioinformatics tools to analyze their functions within proper time. AFPs can be used widely in various aspects of application and have significant industrial functions, encompassing the enhancement of foods’ freezing and liquefying properties, protection of frost plants, enhancement of ice cream’s texture, cryosurgery, and cryopreservation of cells and tissues. In conclusion, these applications and physical properties of AFPs can be further explored to meet other industrial players. Designing the peptide-based AFP can also be done to subsequently improve its function.

Heterologous Gene Expression System Using the Cold-Inducible CnAFP Promoter in Chlamydomonas reinhardtii

To increase the availability of microalgae as producers of valuable compounds, it is necessary to develop novel systems for gene expression regulation. Among the diverse expression systems available in microalgae, none are designed to induce expression by low temperature. In this study, we explored a cold-inducible system using the antifreeze protein (AFP) promoter from a polar diatom, Chaetoceros neogracile. A vector containing the CnAFP promoter (pCnAFP) was generated to regulate nuclear gene expression, and reporter genes (Gaussia luciferase (GLuc) and mVenus fluorescent protein (mVenus)) were successfully expressed in the model microalga, Chlamydomonas reinhardtii. In particular, under the control of pCnAFP, the expression of these genes was increased at low temperature, unlike pAR1, a promoter that is widely used for gene expression in C. reinhardtii. Promoter truncation assays showed that cold inducibility was still present even when pCnAFP was shortened to 600 bp, indicating the presence of a low-temperature response element between -600 and -477 bp. Our results show the availability of new heterologous gene expression systems with cold-inducible promoters and the possibility to find novel low-temperature response factors in microalgae. Through further improvement, this cold-inducible promoter could be used to develop more efficient expression tools.